Volume 111 of the IARC Monographs series, now available from the International Agency for Research on Cancer, evaluates the carcinogenic potential of carbon nanotubes and silicon carbide.
Carbon nanotubes exist in one of two forms: as a single graphene cylinder with an outer diameter of 1–3 nm, which are known as single-walled carbon nanotubes (SWCNT), or as layers of multiple graphene cylinders with diameters of 10–200 nm, which are known as multi-walled carbon nanotubes (MWCNT). An IARC working group evaluated both SWCNT and MWCNT and classified one type of multiwalled carbon nanotube, MWCNT-7, in Group 2B, IARC’s designation for substances that are possibly carcinogenic to humans. The working group based this determination on evidence from studies of experimental animals. Multi-walled carbon nanotubes other than MWCNT-7 as well as single-walled carbon nanotubes were found to be not classifiable regarding their carcinogenicity to humans and were designated as Group 3.
Silicon carbide particles, which are associated with the Acheson process for synthesizing graphite and silicon carbide, were classified as Group 1 based on evidence that they cause lung cancer. The working group designated the fibrous form of silicon carbide as Group 2B. Silicon carbide can also exist in whisker form, which the working group designated as Group 2A, probably carcinogenic to humans. A minority of the working group argued that whiskers and fibers should be evaluated together.